Line-narrowing techniques

Two line narrowing techniques, matrix isolation and resonant laser excitation, are being used separately and in combination to eliminate inhomogeneous broadening (94). Microenvironmental inhomogeneities are reduced by freezing the sample into uniform site locations in isolation or Shpol skii matrices (95). Alternatively, with highly monochromatic and tunable lasers, it is possible to photoexcite only the subset of emitter sites in a low temperature matrix which have... 

An identihcation of the nature of Cr luminescence in synthetic spinel by the line narrowing technique enabled to distinguish up to 25 different Cr + sites (Deren et al. 1996). Laser-induced time-resolved spectroscopy enables us to see typical for spinel emission of Cr ", while the different broadness of the spectral lines at different time windows demonstrates that different Cr " sites are present also in natural spinel (Fig. 4.51). 

In summary, theoretical considerations show that the Hamiltonian operator responsible for the central part of the spectrum when line-narrowing techniques are applied is almost identical to that effective in the liquid state. 

Lochhead and Bray (1995) studied Eu3+ doped sodium disilicate glass with a high-pressure fluorescence line-narrowing technique. This technique was used to characterize the local structure of the Eu3+ ions up to a pressure of 21 GPa. For the crystal-field analysis they assumed a C2v site symmetry which allowed for a complete splitting of the crystal-field components. The crystal-field strength was determined according to eq. (11). The effect of pressure... 

Improvement by a factor of about 10 in the sensitivity of the comparison of theory and experiment for Av appears possible at this time.9 With the use of a chopped muon beam now available at Los Alamos, line narrowing techniques can be employed.10 Use of a higher magnetic field value will improve the accuracy in determining p /pp. Finally, the intensity and quality of the muon beam has been improved since the last measurement. Considering all these factors, a measurement of Av to about 5 ppb and of p /up to 30 ppb appears possible. 

Butler, L. G., Cory, D. G., Dooley, K. M., Miller, J. B. and Garroway, A. N. (1992). NMR imaging of anisotropic solid-state chemical-reactions using multiple-pulse line-narrowing techniques and H-1 T1-weighting. J. Am. Chem. Soc., 114, 125-35. [238]... 

The m.p. line-narrowing technique has added an impressively long list of proton shielding tensors a to our knowledge of material properties. Complementary access to such tensors is to calculate them by quantum chemical methods. An important advantage of this approach is that, in addition to the symmetric constituent of a, it also yields the components of the antisymmetric constituent o " that are virtually inaccessible to measurements by spectroscopic means. So far only relaxation studies have provided experimental information about (Kuhn, 1983 Anet and O Leary, 1992). Note that these experiments were done on carbons. 

Even with the line-narrowing techniques described earlier, NMR experiments on solids with dilute spin- /2 nuclei are still relatively unattractive on two principal counts. One is the lack of sensitivity due to their low net polarisation and the other is the relatively long spin-lattice relaxation time that is often encountered. In solids where both abundant (I) and dilute (S) nuclei coexist, polarisation transfer techniques can usually be used to overcome both these problems. There are many schemes to effect such a transfer but the most common technique is to create and then spin-lock transverse I-magnetisation. This experiment is best understood using ideas from spin thermodynamics. The magnetisation is given by Curie s Law (Eq. 2.21) and the temperature in... 

The rate constant (36) and (37) as a function of temperature correlated well with the experimental data obtained for the carboxylic acid protons of crystalline perprotobenzoic acid and ring-deuterobenzoic acids by nuclear magnetic resonance 7) [75] and inelastic neutron scattering (for an analysis of the experiment see Refs. 76 and 77). It should be noted that some of the major parameters of the model (for instance,. /) allowed the direct determination by fluorescence line narrowing technique. 

Theory of Quadrupolar Spins Line Narrowing Techniques... 

THEORY OF QUADRUPOLAR SPINS LINE NARROWING TECHNIQUES... 

At high cross-link densities the residual dipolar interaction of the protons on the network chains increases, and the linewidth broadens beyond 3 kHz. Then line-narrowing techniques from solid-state NMR, such as MAS and multi-piil.se excitation must be applied to reduce the ani.sotropy of the dipole-dipole interaction during the space encoding steps of the imaging sequence. In this way, signal-to-noise ratio as well as spatial resolution can be improved jCorll. 

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